地球科学と気候変動ジャーナル

抽象的な

Spatial Variation of Nutrients in Sondu-Miriu and Simiyu-Duma Rivers: Implication on Sources and Factors Influencing their Transportation into the Lake Victoria

Said A. H. Vuai, John D. Ibembe and Nancy Mungai

Lake Victoria basin has been under growing pressure from both natural and anthropogenic activities. These activities have created many nutrient pollution sources which affect the survival and sustainability of the Lake Ecosystem. This study was conducted to investigate the transportation of nutrients into the Lake Victoria through the Sondu-Miriu (SM) and the Simiyu-Duma (SD) rivers to represent the changes that have been occurring in many rivers draining the Lake basin. Water samples were collected along the SM and the SD river courses from upstream to the Lake shore. The results showed that the concentration of nitrate ranged between 770 μgL^-1 and 970 μgL^-1 for SM River and between 400 μgL^-1 and 1250 μgL^-1 for SD River while for phosphate it ranged from 120 μgL^-1 to 270 μgL^-1and from 457 μgL^-1 to 1175 μgL^-1 for SM and SD Rivers, respectively. The estimated nutrient loading through SM were 40ty^-1 and 7.9ty^-1 while for SD River were 25 ty^-1 and 26ty^-1 for dissolved inorganic nitrogen and phosphorous, respectively. The spatial variation of the concentrations nitrogen was not significant along the SM while in the SD Rivers the average concentration was lower in downstream than in the middle due to presence of swamp and dam that regulate the flow of water and retain nutrients. The results suggest that the catchment soil and rock are the major sources of the nutrients and their interaction with water dominate the transportation mechanism of the nutrients to the Lake Victoria through the Sondu-Miriu and Simiyu-Duma rivers.